Functional encryption and attribute-based encryption are public key encryption schemes according to which a set of users authorized to decrypt a ciphertext can be set in the ciphertext with a logical expression composed of OR, AND, and NOT. That is, functional encryption and attribute-based encryption are public key encryption schemes according to which a decryption condition of a ciphertext can be set in the ciphertext with a logical expression composed of OR, AND, and NOT. Patent Literature 1 describes a functional encryption scheme.
There is a technique called proxy re-encryption according to which a decryption condition set in a ciphertext can be changed using a re-encryption key without decrypting the ciphertext. Non-Patent Literature 1 describes a proxy re-encryption scheme in functional encryption. Non-Patent Literature 2 describes a proxy re-encryption scheme in attribute-based encryption.